1. Field of the Invention
The present invention relates to the field of sampling gaseous fluids such as exhaust gases from thermal combustion engines in order to analyse them.
More precisely, the present invention relates to the sampling of gaseous fluids containing aldehydes and ketones, as well as hydrocarbons.
According to the invention, these two sampling methods can be carried out simultaneously or not, according to a selected analytic objective.
2. Description of the Prior Art
To date, most analysis laboratories performing individual aldehyde, ketone and hydrocarbon measurements in the exhaust gases of motor vehicles on chassis dynamometers work with their own measuring equipment, without any interactive connection between these various elements, i.e. without a really reliable, accurate and reproducible sampling protocol.
As regards aldehyde and ketone emissions, dinitrophenylhydrazine-grafted silica cartridges for sampling and chemically deriving these chemical species to hydrazone compounds are currently the most commonly used ones. Each cartridge must afterwards be subjected to a treatment in the analysis laboratory in order to dissolve these compounds in a solvent (acetonitrile). This sampling technique has the advantage of being effective, easy to use and it offers possibilities of medium-term storage of the samples. The hydrazone derivatives are then separated by injecting an aliquot of this solution into a HPLC (High-Performance Liquid Chromatography) unit and detected individually by UV (ultraviolet) absorption.
There is no compact commercial equipment using such cartridges and allowing the carrying out of the necessary stages of a sampling protocol such as control, monitoring and recording of the sampling parameters required for reliable and accurate quantification of the aldehyde and ketone emissions.
Concerning individual C1-C13 hydrocarbon emissions, and in order to have standard sampling conditions similar to those under which sampling of conventional pollutants (CO, total HC, NO.sub.x) is carried out, Tedlar (chemically inert and plasticizer-free polyvinyl chloride film) storage bags are commonly used. These bags are generally installed in parallel with existing equipments in order to provide a certain representativeness of the diluted effluent supplied during the working cycle.
Other known methods transfer, after the tests, the gases collected in the sampling bags to smaller bags (10 to 20 litres) in order to convey them more readily to the analysis laboratory. A small volume is then injected into a gas chromatography unit according to particular analytic protocols (injection by calibrated loop, reconcentration of the sample on solid supports, . . . ). Sometimes, the gaseous effluents discharged by a diesel vehicle are not filtered, which pollutes the bags for good. In other known cases, filtering is such that hydrocarbon retention can lead to hydrocarbon-containing compound losses, notably those lower than C13.
There is no known equipment for sampling specific pollutants such as aldehydes, ketones, hydrocarbons, allowing sampling according to standard working cycles.